This page compares the sensitivity of JWST’s instruments to those of current observatories. The purpose is to help astronomers visualize JWST’s capabilities, and how JWST will advance their own science.

There are many ways to measure performance: limiting point source flux, limiting line flux; time to survey a given area of the sky or number of spectroscopic targets; and so on. We select illustrative simple cases for fairly short (10,000s) integrations. For other scenarios, users can scale from the data tables below, or use the JWST Exposure Time Calculators.

Where the numbers come from: JWST sensitivities used here are requirements: the minimum performance required of each instrument. This is a conservative approach; the on-orbit performance may be better.

Sensitivities for other observatories are taken from instrument handbooks, online calculators, and published papers, as documented in the data tables. If a user believes they have discovered an error in these sensitivities, they are requested to contact Jane.R.Rigby@nasa.gov.

Photometric performance

Plotted is the faintest flux for a point source that can be detected at SNR=10 in a 104 s integration. Fluxes are given in Janskies as well as AB magnitudes.

Spectroscopic performance (R=600-3000)

Plotted is the faintest line flux that can be detected at SNR=10 in a point source in a 104 s integration.

Symbols are as follows:

-Red squares show the required performance of NIRSpec at R=2700, the required performance of MIRI in medium resolution mode (R=2400 to 1200), and the expected performance of the NIRCam grisms at R=1000..

-Red curves show the predicted performance of NIRSpec at R=2700 (upper set of curves) and R=1000 (lower set of curves).

-Black squares show IRS on Spitzer, with the SH and LH gratings at R~600.